1. Field of the Invention
The present invention relates to a method for introducing and making foreign microorganisms survive in an ecological system such as waste water or soil in which various kinds of microorganisms coexist. More specifically, it relates to a method for survival of foreign microorganisms without replenishing the foreign microorganisms or nutrients, as well as a method to efficiently remedying the environment using the above-mentioned method in water treatment and soil remediation etc.
2. Related Background Art
In the field of waste water treatment, processes have been widely carried out to decompose target substances using activated sludge in which the activity of microorganisms is utilized. Furthermore, for the remediation of the polluted soil or polluted ground water, it has been attempted to introduce the microorganisms capable of degrading pollutants into the polluted area to remedy it.
The microorganisms, however, are generally passive to the environment and often sensitive to the given environment. They can not immediately adapt themselves to the given environment and the degradation activity is often lost or extinction may occur. In an ecosystem comprising plural kinds of microorganisms, it is observed that the niches of the ecosystem are already occupied by the various kinds of originally living microorganisms, and these native microorganisms do not easily permit the survival and growth of newly introduced foreign microorganisms.
In these cases, the foreign microorganism introduced into waste water or soil can not adapt to the new environment, and the population of the microorganism rapidly decreases resulting in little decomposition of a target substance. Otherwise, when the foreign microorganism adapts to the new environment at first, the population of the microorganism may decrease later due to the change of various environmental factors, so that the function of degradation and detoxification deteriorates or ceases to work entirely. For example, if a substance harmful to microorganisms is mixed into waste water, the activity of the activated sludge deteriorates and the target substance cannot be degraded any more. Even if the microorganisms having the degradation ability are newly introduced to restore the pollutant degradation ability of the activated sludge, it is difficult for the introduced microorganisms to squeeze themselves into the niches to live and grow, in the ecosystem already occupied by the various kinds of originally existing microorganisms.
If the target ecosystem is soil or the soil-water system including ground water, the interaction between the microorganisms and environmental components is stronger than in the activated sludge. Therefore, when the foreign microorganisms are introduced into such a system by an ordinary method, it is more difficult for the foreign microorganisms to stably grow in the ecosystem and maintain their concentration necessary for the degradation of the pollutants.
In order to compensate the reduction of the degradation microorganisms, usually the system such as a septic tank or soil is supplemented with an excessive amount of the degradation microorganisms to increase the amount of the decomposing microorganisms. Furthermore, in order to secure the good growth of the introduced microorganism, the ecosystem is replenished with components containing nutrients for the introduced microorganisms and oxygen gas to promote their growth and to increase the amount of the introduced microorganisms.
As stated above, when foreign microorganisms are introduced into an environment such as a septic tank or soil in this manner, there is a problem that the population of the introduced microorganisms decreases rapidly and as a result, the function of degradation and detoxification is lost. Supplementing the foreign microorganisms, nutrients, oxygen and the like as a measure to address this problem is time-consuming, and raises the cost when the foreign microorganisms and the nutrients are expensive. Moreover, since the reduction of the foreign microorganisms may occur at any moment, the population of the foreign microorganisms and the degradation ability of the microorganisms should be frequently measured to quantitatively determine the timing of replenishing the foreign microorganisms and the nutrients, and hence this method is very troublesome in practice.